Separation and identification of cations in mixtures

The separation scheme below was first outlined by R. Fresenius in 1841, though in the course of time modifications were introduced. Before attempting such a task, it is necessary to test for ammonium ions in the original sample (cf. Section 5.3 (3)). During the course of separations most of the reagents are added in the form of ammonium compounds thus by the time Group V is reached, a considerable amount of ammonium ions have built up in the test solution. 

Separations are carried out according to the scheme outlined in Tables 

1 to 5.10. Note that it is important to verify the presence of a given cation by further tests. 

Separation of cations into groups (Anions of organic acids, borates, fluorides, silicates, and phosphates being present). Add a few drops of 2m HCl to the cold solution. If a precipitate forms, continue adding 2m HCl until no further precipitation takes place. Filter. 

Add 1 ml of 3% H2O2 solution. Adjust the HCl concentration to 0.3m. Heat nearly to boiling, and saturate with H2S under pressure . Filter. 

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